Alzheimer's disease (“AD”) is a neurodegenerative disorder characterized by the occurrence of amyloid plaques, neurofibrillary tangles and significant neuronal loss. β-Amyloid protein (also referred to as the Aβ peptide), the main component of senile plaques, has been implicated in the pathogenesis of Alzheimer's disease (Selkoe (1989) Cell 58:611-612; Hardy (1997) Trends Neurosci. 20:154-159). β-Amyloid has been shown to be both directly toxic to cultured neurons (Lorenzo and Yankner (1996) Ann. NY Acad. Sci. 777:89-95) and indirectly toxic through various mediators (Koh et al. (1990) Brain Research 533:315-320; Mattson et al. (1992) J. Neurosciences 12:376-389). Additionally, in vivo models, including the PDAPP mouse and a rat model have linked β-amyloid to learning deficits, altered cognitive function, and inhibition of long-term hippocampal potentiation (Chen et al. (2000) Nature 408:975-985; Walsh et al. (2002) Nature 416:535-539). Therefore, a great deal of interest has focused on therapies that alter the levels of β-amyloid to potentially reduce the severity or even abrogate the disease itself.
One AD treatment strategy that has recently emerged in response to successful studies in PDAPP mouse and rat experimental models, is that of immunization of individuals to either provide immunoglobulins such as antibodies (as in the case of passive immunization, wherein therapeutic immunoglobulins are administered to a subject) or to generate immunoglobulins (active immunization, wherein the immune system of a subject is activated to produce immunoglobulins to an administered antigen) specific to β-amyloid. These antibodies would in turn help reduce the plaque burden by preventing β-amyloid aggregation (Solomon et al. (1997) Neurobiology 94:4109-4112) or stimulating microglial cells to phagocytose and remove plaques (Bard et al. (2000) Nature Medicine 6: 916-919). Further by way of example, a humanized anti Aβ peptide IgG1 monoclonal antibody (a humanized 3D6 antibody) can effectively treat AD by selectively binding human Aβ peptide.
For a protein, and in particular, an antibody, to remain biologically active, a formulation must preserve intact the conformational integrity of at least a core sequence of the protein's amino acids while at the same time protecting the protein's multiple functional groups from degradation. Degradation pathways for proteins can involve chemical instability (i.e., any process which involves modification of the protein by bond formation or cleavage resulting in a new chemical entity) or physical instability (i.e., changes in the higher order structure of the protein). Chemical instability can result from deamidation, racemization, hydrolysis, oxidation, beta elimination or disulfide exchange. Physical instability can result from denaturation, aggregation, precipitation or adsorption, for example. For a general review of stability of protein pharmaceuticals, see, for example, Manning, et al. (1989) Pharmaceutical Research 6:903-918. In addition, it is desirable to maintain stability when carrier polypeptides are not included in the formulation.
While the possible occurrence of protein instabilities is widely appreciated, it is impossible to predict particular instability issues for a particular protein. Any of these instabilities can potentially result in the formation of a polypeptide by-product or derivative having lowered activity, increased toxicity, and/or increased immunogenicity. Indeed, polypeptide precipitation can lead to thrombosis, non-homogeneity of dosage form and immune reactions. Thus, the safety and efficacy of any pharmaceutical formulation of a polypeptide is directly related to its stability.
Accordingly, there continues to exist a need for formulations that not only maintain the stability and biological activity of biological polypeptides, for example, Aβ binding polypeptides, upon storage and delivery, but are also suitable for various routes of therapeutic administration.